Using chronograph data to determine the best load????

[Derek M.]

[ QUOTE ]
Then there's the issue that no two people will get the same muzzle velocity with the same rifle and ammo. There can be 80 to 100 fps difference caused by how they hold the rifle.

[/ QUOTE ]

I must admit when I read this the first thought was this statement defies the physics of ballistics. I've never seen this at all and I've been shooting through a chronograph for 15+ years. I've had over a dozen guys shoot my rifle at a range in addition to my 12 year old nephew and I've never witnessed any such incidence. Maybe it happened to you randomly, perhaps there's a logical explanation. Maybe someone shot a round where the powder thrower didn't release the exact powder charge that it should have, then the next round dumped too much, or more than was supposed to be, but the way a rifle is supported has nothing to do with the lock time, ignition, powder burn rate, and internal ballistics until the bullet leaves the muzzle.

Maybe the chrono didn't read accurately that day. Who knows, but I respectfully disagree with the message.

 

[green 788]

We've headed off in a couple or three different areas here, but it's shaping up to be an interesting discussion.

BH, I don't recall us discussing the OCW load development method, but that's my fault. I've got a bad memory sometimes.

You seem like you do find credence in the ladder method (Audette method), which is why I'm puzzled that you don't believe the OCW method is useful. In truth, the OCW method is a modified Audette method, and statistically much more meaningful than any number of ladder tests one might want to shoot. The OCW method allows for the variations of warming and fouling barrels, changing conditions, and even a tiring shooter--as it seeks to spread the error factor evenly across all of the tested charge weights.

There simply are not that many true accuracy nodes for any given powder and bullet combo. I'd say it's extremely rare to find more than two true accuracy nodes within reasonable pressure levels (starting and max loads). That isn't to say that you won't find some powder charges which shoot very well--so long as they are carefully weighed, and poured into perfectly prepared brass with bullets seated just so--but those are not true accuracy nodes.

Not to impugn you personally--as I'm sure you're up to speed on many aspects of shooting and handloading--but I have found an astonishing amount of ignorance in BR circles as to what is and is not important. Some BR guys buck the system, such as Richard Schatz who doesn't neck turn or uniform primer pockets or shoot a twenty pound rifle--but still manages to have the 6-target NBRSA 1000-yard Light Gun World Record (shooting a 6mm Dasher). Or Tim Lambert, who put together a Savage actioned 7mm WSM and, with less than a grand invested in the whole rig, fired a world record 1 mile group. Such guys are not common. Most folks in the craft continue to suck the pablum of whatever everyone else tells them will and won't work--which is why you see so much conformity.

While I recognize the two guys above as the winners that they indeed are, it is still not prudent to assume that just because a guy is a good trigger man that he necessarily knows all there is to know about load development. There are excellent race car drivers who will hold up a bottle of STP oil treatment and smile for the camera--all the while knowing very little about engine lubrication.

One last thing. OCW load recipes don't have to be limited to 1/2 MOA. One can alter the seating depth of the bullet and/or try different primers to tune the group even smaller. So I'm not sure where the notion that OCW load recipes are good for 1/2 MOA and no more comes from. That's just not true.

Dan

 

[Derek M.]

[ QUOTE ]
I'm not sure what the actual velocity difference would be, but yes, if one guy free recoils a rifle and another holds it firm against his shoulder, there will be a difference in the distribution of the cartridge's energy. In the free recoil situation, some of the energy of the burning powder is going into pushing the rifle backwards, and this leaves less energy to propel the bullet forward.

Try this next time you use your chronograph. Shoot a few free recoil (if possible) or with a light hold versus firm. You'll almost certainly see some different numbers...

Dan

[/ QUOTE ]

Not in my case. The difference in forces generated in recoil from person to person are negligible when the individuals are still supporting the rifle to a degree. I've never seen this.

Shouldn't the same occur if you shoot a rifle with and without a muzzlebreak? The forces are distributed differently in those cases too but our velocities remain constant.

 

[green 788]

Derek,

I'm not going to vehemently assert that this is fact. It appears to have been the case from my own observations in the past--especially with pistols--but those are isolated issues, admittedly.

An old engineering trick, when trying to understand what the reaction to some small change might be, is to mentally exaggerate the change. This in turn often sheds some light on what is likely to happen.

I once debated a guy who claimed that faster barrel twists would not cause increased chamber pressures. I asked him how a 1:2 twist might affect pressure, and he quickly back peddled, saying something like "within normal twist offerings chamber pressure differences won't be noticed." But I believe that he finally conceded that faster twists would--to at least some degree--increase chamber pressures when all else was equal.

But as to the free-recoil, firm hold and its relation to MV...

If the rifle moves back at about 4 feet per second (which would seem nominal), how might that affect muzzle velocity? How much energy does it take to propel a 9 pound rifle backward at 4 feet per second? And how much might that add to the forward momentum of the bullet?

What causes the rifle to move backwards in the first place? Well, it is the force which is pushing against the base of the bullet. If the rifle is prevented from moving backwards, where does that energy go? I would say it is added to the propulsion of the bullet. That's the only place it could go, isn't it?

You guys know what... /ubbthreads/images/graemlins/smile.gif I have tomorrow off. Maybe I'll take a couple rifles to the range tomorrow and see what happens. Anyone else have some time and ammo to waste for the cause? /ubbthreads/images/graemlins/laugh.gif

Dan

 

[bailey1474]

[ QUOTE ]
What causes the rifle to move backwards in the first place? Well, it is the force which is pushing against the base of the bullet. If the rifle is prevented from moving backwards, where does that energy go? I would say it is added to the propulsion of the bullet. That's the only place it could go, isn't it?


[/ QUOTE ]

No. The energy is still transferred rearward. Just b/c the rifle doesn't move, doesn't mean that no energy was transferred. Do you think a person pushing on a wall will not get tired even though the wall doesn't move? They will get just as tired or more so than someone moving an object. The rifle doesn't have to move backward for the energy to be transferred. Look up the defenitions of work and energy and you will see what I am talking about.

 

[green 788]

Fair enough, Bill. I will do my level best to get to the range tomorrow with at least two rifles and some tight shooting handloads, and see what I come up with. Not promising, but I'll definitely put it on my agenda for tomorrow.

Maybe some others of you can get time to test the idea too, so we'll have more results to compare... /ubbthreads/images/graemlins/smile.gif

Dan

 

[BountyHunter]

Dan

we discussed this in detail last year on snipershide. It is just that I have found that the audette/ladder with chrono works extremely well, no questions asked. Will the OCW give that much info w/o using a chrono, I do not see how, but obviously it works to some degree. So yes it works but not to the level that I see that I can get the same information with the same number of shots.

It is not uncommon for magnums to give their best accuracy as much as 150-200 fps below top end. So it is common to get up to 4 nodes on a barrel over 200 fps spread. THe norm is really 2-3 though.

YOu are correct that we often see the one group wonder in this sport, but it is more telling how often they finish in top 10 and how consistent they are. I was 9th for points last year and I only had the chance to shoot 3 matches this year. Took , 4th in LG and 10 in HG at the PA world open and won my relay at the other match, just got beat by smaller groups in the final. The 4th at World open was with new LG that was shooting its first match at 1000 after ladder testing and tweaking of less than 60 rds at 300 yards starting 3 days before the match. So yes, the ladder works extremely well.

But like I said to each his own.

Bart you will never find me saying anything about the accuracy of a M70. I have built up a couple shooters and the first IBS guy to reach 100 match points (last year) shoots a 98 and M70 actions and does his own smithing, so I know real well what they can do.

BH

 

[Derek M.]

[ QUOTE ]
I once debated a guy who claimed that faster barrel twists would not cause increased chamber pressures. I asked him how a 1:2 twist might affect pressure

[/ QUOTE ]

I think the pressure would be less as a 1:2 twist would probably just strip the bullet of copper instead of imposing any rifling at all. /ubbthreads/images/graemlins/tongue.gif

I have a police officer friend that is a gunsmith too. He likes to play at the range whenever possible. I'll ask him to check out the info contained in this thread and see what he comes up with.

Don't get me wrong, I'm not saying "I'm right and you're wrong." I just haven't witnessed anything like this at all in my years of rangetime and shooting in what appears to be similar variables.

 

[uncleB]

BartB & green788,
If you are talking about 100-200 or even up to 600yards ,I can listen to and try and understand your debate. at 1000yds out you have no basis other than in lunacy.
UB

 

[bailey1474]

I'll try it sometime as well. It will be a while before I break the chrono out again though. Let us know what you find. As long as the rifle is stationary on ignition, the velocities should remain constant(I hope, or else I'm going to look like an idiot /ubbthreads/images/graemlins/blush.gif).

 

[RDM416]

Bill,

I have been watching the posts with interest about the effect of a light hold versus a firm hold and the impact this would have on velocity.

I agree with you that it should have no effect under normal conditions. Normal conditions being a rifle of typical weight, let's say, 8lbs and up. (I am giving my opinion here guys and could be proven wrong)

While I don't claim to be a full fledged physicist, I am an electronic engineer with a significant background in phisics both classroom and practical.

You are correct about "work" if the gun does not move that means no "work" has been accomplished but it does not mean that no energy has been expended. Energy can be expended in other ways than movement, heat for example.

It takes a very short time for a bullet to exit a barrel. A bullet traveling at 3000fps will take .000722 seconds to exit a 26" barrel. /ubbthreads/images/graemlins/blush.gif Due to the mass of the rifle there will have been no significant movement (recoil) at this point. High speed photography will prove this. Also consider that if the movement of the rifle recoiling has an effect on velocity, logicaly that could only be true if the rifle began to move BEFORE the bullet exited the barrel. If that were the case accuracy would impossible to obtain due to the movement of the entire rifle which would very erratic. So, logic as well the previously mentioned photography would suggest that since the bullet has left the barrel before the rifle begins to recoil, that there would be no effect on velocity.

That said............we return to the question of mass. There must be enough mass in the form of the rifle to create this effect. For example: if one were to to take a short section of a lightweight barrel and manage to affix a loaded cartridge in it and fire it with nothing to hold it, the barrel section would go one way and the bullet at a signficantly reduced velocity would go the other. This is because the mass of the fixture would not be great enough to hold it in place until the projectile has exited the barrel.

It has been too many years since I have tried to work through this kind of physics and I am not motivated enough to go dig out my old books and figure it out. But MY OPIONION is that the mass of a typical rifle is enough to hold it stationary long enough for the bullet to exit the barrel. At this point, recoil is the residual effect of the explosion that propelled the bullet. However, I do not claim to be able to quanitify how much mass is required in the rifle to cause this effect versus the other extreme example I gave above.

And I could be totally wrong. /ubbthreads/images/graemlins/crazy.gif I hope someone on this site is a little more up to date on his physics and can help us put the question to rest.

Well that should have muddied the water up a little! /ubbthreads/images/graemlins/grin.gif

 

[Eaglet]

RDM416,
In all truthfulness, I'm pretty ignorant in spite of having 3.5 years of full time Civil Engineering schooling years ago. That said, I believe many would find hard to believe, including my self, that recoil takes place after the bullet has come out regardless of how fast it may come out! For every action there is a reaction... or should I say for every action there is an instant reaction? If recoil is after the bullet comes out, then why we pay so much attention to consistency, how to hold the rifle, how much cheek pressure, how we pull the trigger, etc and etc. If the bullet comes out first then all the other would be useless. Differences in butt pressures makes different bullet behavior from shot to shot, again if bullet comes out before recoil it should not make any difference! Should it?

 

[Bart B]

RDM416, you said:

"It takes a very short time for a bullet to exit a barrel. A bullet traveling at 3000fps will take .000722 seconds to exit a 26" barrel. Due to the mass of the rifle there will have been no significant movement (recoil) at this point."

Maybe you can also explain why large caliber double rifles should not have their muzzle centers 1/4th to 3/8ths closer together than their breech centers. That's over 30 minutes of angle. They're regulated this way so both barrels shoot to the same point of impact. If those 13-pound rifles didn't move sideways during the time the bullet was going down a barrel, at 50 yards bullets from both barrels would strike over 15 inches apart. That doesn't happen. 'Smiths get paid good money to braze both barrels together at the proper angle so they do "regulate" and shoot to the same point of aim.

 

[green 788]

Well, as mentioned earlier, I believe that I've seen this effect when chronographing factory handgun ammuntion, in 9mm and 45 ACP. The 9mm was a Glock 26, so its being a relatively light pistol propelling a relatively powerful cartridge may have exacerbated this effect.

It's rainy and wet here today, but I still plan on getting to the range with a fresh battery in the Chrony. And probably a .308, a 6.5 x 55, and yes, a 45 ACP.

More as it comes... /ubbthreads/images/graemlins/smile.gif

Dan